Editor's Note: (Gayle Tzemach Lemmon is a senior fellow at the Council on Foreign Relations and the author of New York Times best-sellers "Ashley's War: The Untold Story of a Team of Women Soldiers on the Special Ops Battlefield" and "The Dressmaker of Khair Khana." You can follow her work at gaylelemmon.com and on Twitter at @gaylelemmon. The opinions expressed here are her own.)
(CNN) Sameera Allam says her heart breaks when she thinks about her teenage son, who goes off to work each morning doing whatever job he can get to help support his family.
In Syria, he went to school.
But that was before the war. And before her family was forced to flee violence in Aleppo for the safety of Turkey. The Syrian conflict -- now on the verge of its sixth year -- has stripped them of their home, their livelihood and their country.
Her son cries each day and tells her he just wants to get back to his studies.
"What do you do when your son cries and says he wants to go to school?" I asked her at a community center run by the Turkish NGO Association for Solidarity with Asylum Seekers and Migrants in Gaziantep, Turkey, a half-hour's drive from the Syrian border.
"I cry, too," she said. "We are crying together."
She is hardly alone. As UNICEF noted recently, "Nearly five years into the crisis, around 4 million children" are out of school. More than 2 million of these children remain inside Syria, where the war rages on, and 700,000 are in the nations which have taken the bulk of Syria's 4 million-plus refugees: Turkey, Lebanon, Jordan, Iraq and Egypt.
An entire generation of young Syrians is out of school and desperate for education. And the world will pay the consequences if nothing is done to help them.
"Education represents the hopes, dreams and aspirations of children, families, communities and nations around the world -- the most reliable route out of poverty and a critical pathway towards healthier, more productive citizens and stronger societies," according to a 2015 UNESCO report on education.
Speak with Syrian children living as refugees in southern Turkey, and one of the first topics of conversation is school. Those who are in it tell you their favorite subjects. Those who aren't talk about how they want to go.
Still, millions of Syrian children have no chance to sit in a classroom. Many are sent to work. Some are left to their own devices. Walk through the streets of many Turkish towns and you are sure to see Syrian children, who once went to school, playing in the streets or serving as laborers to help their families earn enough money to cover the costs of food, rent and basic survival.
Khaled is one of the lucky ones. The 12-year-old lost his father to the war and his mother -- a teacher back in Syria -- led her children to safety in the Turkish border town of Kilis after a harrowing escape from Aleppo.
"What are your favorite subjects?" I asked when I learned he was in school.
"English and Arabic," he said in Arabic. And then he practiced his skills.
"Hello, my name is Khaled," he said in English, beaming with pride.
But stories like Khaled's remain all too rare. For girls the situation is especially dire. Families who have fled to Syria's neighbors worry about their daughters' safety and are often reluctant to send them to schools that are not within close walking distance. School fees are also an issue -- if classrooms will even open to refugee children.
This means girls are often confined to their homes, where their safety can be monitored. Some parents turn to child marriage, an option they say they view as a way to make sure their girls are protected, or a best option in the face of no other ones.
The mother of a 15-year-old girl I met at a community center run by the charity Mercy Corps told me that suitors come to their home regularly to seek her daughter's hand, but she is determined that her daughter will find a way to learn and to have a better future. Her daughter, who dreams of becoming an English teacher, is among the fortunate ones. Recently the charity CARE told Australia's ABC News it is seeing a "massive increase in child marriage" and found that between 2011 and 2014 the number of forced marriages in the Syrian refugee population in Jordan tripled among girls aged 15 to 17.
"This is a tragedy for the young girls," says Muzaffer Baca, vice president of the International Blue Crescent Relief and Development Foundation, an organization aiding Syrians in Turkey by providing services including schools, job training and medical care. He says he has frequently heard men talking of taking Syrian girls as brides. At first, he says, he was surprised to hear such conversation, but no longer.
"In Saudi Arabia, (people are) even joking with me, why you don't have your second or third wife?" Baca says.
All this suffocated human potential will have consequences, Baca says.
"Our future are the children," he says. "If we want a good generation we have to educate them, we have to keep them healthy psychologically and physically."
If not, says Baca, we will all pay.
"Syria's young generation is lost," Baca says. "You will see what will happen in the future."